The present disclosure relates, in general, to ultrasonic surgical instruments and more particularly to ultrasonic transducers to drive ultrasonic blades. Ultrasonic instruments, including both hollow core and solid core instruments, are used for the safe and effective treatment of many medical conditions. Ultrasonic instruments, and particularly solid core ultrasonic instruments, are advantageous because they may be used to cut and/or coagulate organic tissue using energy in the form of mechanical vibrations transmitted to a surgical end effector at ultrasonic frequencies. Ultrasonic vibrations, when transmitted to organic tissue at suitable energy levels and using a suitable end effector, may be used to cut, dissect, elevate or cauterize tissue or to separate muscle tissue from bone. Ultrasonic instruments utilizing solid core technology are particularly advantageous because of the amount of ultrasonic energy that may be transmitted from the ultrasonic transducer, through a waveguide, and to the surgical end effector. Such instruments may be used for open procedures or minimally invasive procedures, such as endoscopic or laparoscopic procedures, wherein the end effector is passed through a trocar to reach the surgical site.
Activating or exciting the end effector (e.g., cutting blade) of such instruments at ultrasonic frequencies induces longitudinal vibratory movement that generates localized heat within adjacent tissue. Because of the nature of ultrasonic instruments, a particular ultrasonically actuated end effector may be designed to perform numerous functions, including, for example, cutting and coagulation. Ultrasonic vibration is induced in the surgical end effector by electrically exciting a transducer, for example. The transducer may be constructed of one or more piezoelectric or magnetostrictive elements in the instrument hand piece. Vibrations generated by the transducer are transmitted to the surgical end effector via an ultrasonic waveguide extending from the transducer to the surgical end effector. The waveguide and end effector are designed to resonate at the same frequency as the transducer. Therefore, when an end effector is attached to a transducer, the overall system frequency is the same frequency as the transducer itself.
The amplitude of the longitudinal ultrasonic vibration at the tip, d, of the end effector behaves as a simple sinusoid at the resonant frequency as given by:d=A sin(ωt)where:
ω=the radian frequency which equals 2π times the cyclic frequency, f; and
A=the zero-to-peak amplitude.
The longitudinal excursion of the end effector tip is defined as the peak-to-peak (p-t-p) amplitude, which is just twice the amplitude of the sine wave or 2 A. Often, the end effector can comprise a blade which, owing to the longitudinal excursion, can cut and/or coagulate tissue. U.S. Pat. No. 6,283,981, which issued on Sep. 4, 2001 and is entitled METHOD OF BALANCING ASYMMETRIC ULTRASONIC SURGICAL BLADES; U.S. Pat. No. 6,309,400, which issued on Oct. 30, 2001 and is entitled CURVED ULTRASONIC BLADE HAVING A TRAPEZOIDAL CROSS SECTION; and U.S. Pat. No. 6,436,115, which issued on Aug. 20, 2002 and is entitled BALANCED ULTRASONIC BLADE INCLUDING A PLURALITY OF BALANCE ASYMMETRIES, the entire disclosures of which are hereby incorporated by reference herein, disclose various ultrasonic surgical instruments.
It may be recognized that the effectiveness of an ultrasonic surgical instrument may be related in part to the amount of the longitudinal excursion of the end effector tip. An ultrasonic surgical instrument having an end effector tip capable of a large longitudinal excursion can accomplish more work during a surgical procedure. Consequently, it may be useful to design components of the ultrasonic surgical instrument to maximize the potential excursion of the end effector tip. Further, because there may be some error in the driving frequency produced by the energy source used to power the ultrasonic surgical instrument transducer, it may further be useful to design components of the ultrasonic surgical instrument that may increase the tolerance of the device to such frequency errors.